CN1191002A - Process for preparing reduced odor and improved brightness individualized polycarboxylic acid crosslinked fibers - Google Patents

Abstract

Disclosed is a process for making reduced odor individualized, crosslinked fibers which includes the steps of providing cellulosic fibers, contacting the fibers with a solution containing a C2-C9 polycarboxylic acid crosslinking agent, mechanically separating the fibers into substantially individual form, drying the fibers and reacting the crosslinking agent with the individualized fibers to form intrafiber crosslink bonds. The individualized cellulosic fibers are then contacted with a strong alkaline solution and strong oxidizing agent to reduce the odor and increase the brightness. Preferably, the crosslinking agent is citric acid, and preferably, between about 1.0 weight % and about 12.0 weight % of the crosslinking agent reacts to form the intrafiber crosslink bonds. Preferably, the alkaline solution is an aqueous solution of sodium hydroxide, and preferably, about 0.09 weight % of the sodium hydroxide, on a dry fiber weight basis, is applied to the crosslinked fibers. Preferably, the oxidizing agent is hydrogen peroxide, and preferably, about 0.04 weight % of the hydrogen peroxide, on a dry fiber weight basis, is applied to the crosslinked fiber. The reduced odor individualized, crosslinked fibers are useful in a variety of absorbent structure applications.

Description

Smell reduces the preparation method of brightness single fiber that improve, polycarboxylic acid crosslinked

The present invention relates to have the cellulose fibre of high absorption of fluids performance, the absorbing structure that forms by this cellulose fibre, and the method for preparing this fiber and structure.More specifically, the present invention relates to smell and reduce brightness single fiber cellulose fiber that improve, polycarboxylic acid crosslinked, prepare the method for this fiber, and the absorbing structure that contains the cellulose fibre of single, cross-linked form.

Be known in prior art with the crosslinked fiber of single form basically and the several different methods of this fiber of preparation.Term " single cross filament " is meant the cellulose fibre that mainly has chemical crossbond in the fiber.That is to say that cross-bond mainly is between the cellulosic molecule of a fiber, rather than between the cellulosic molecule of different fibers.It has been generally acknowledged that single cross filament is applicable to the application of absorbent article.Fiber itself and the absorbing structure that contains single cross filament show improvements at least with respect to common noncrosslinking fiber on important absorbent properties.Usually, absorbefacient improvement illustrates with absorptive capacity.In addition, the absorbing structure that is made by single cross filament is with respect to the absorbing structure that is made by the non-crosslinked fiber, and its Wet-resilient and dried resilience are improved.After this term " resilience " is meant the pad made by the cellulose fibre recovery capacity to the initial bubble state when pressure discharges.Dried resilience specifically is meant when fiber is in drying condition basically, the swelliong power of absorbing structure when applied pressure discharges.Wet-resilient specifically is meant when fiber during in wetting conditions, the swelliong power of absorbing structure when applied pressure discharges.For the present invention and disclose conforming purpose,, should observe and report its Wet-resilient for the absorbing structure from wetting to saturated.

According to reports, the preparation method of single cross filament has three kinds usually.These methods that describe below are called the dry crosslinking method here, aqueous solution cross-linking method and substantial non-aqueous solution cross-linking method.

The method of the single cross filament of dry crosslinking prepared is disclosed among the U.S.P 3224926 that 1965.12.21. is issued to L.J.Bernardin.The preparation of single cross filament is by with the plain dried cover plate of crosslinking agent jet fiber, use the mechanism defibre, makes fiber generation when being single state basically crosslinked at dried fibres under the temperature that raises gradually.The result of dehydration before crosslinked, fiber is crosslinked naturally under the state of non-swelling, shrinkage.Illustrated among the U.S.P3224926, wherein crosslinked method takes place in fiber under the state of non-swelling, shrinkage, is called the method for preparation " dry crosslinking " fiber.The fiber of common dry crosslinking seems by cross-bond and highly hardens, and the absorbing structure that makes thus shows higher relatively Wet-resilient and dried resilience.Another feature of dry crosslinking fiber is that fluid retention (FRV) is low.

The method for preparing aqueous solution cross filament for example is disclosed among the U.S.P3241553 that 1966.3.22 is issued to F.H.Steiger.The preparation of single cross filament is by in the aqueous solution that contains crosslinking agent and catalyst that fiber is crosslinked.After this Zhi Bei fiber is called " aqueous solution is crosslinked " fiber by this way.Because the swelling action of cellulose fibre in water, aqueous solution cross filament is crosslinked under the state of non-shrinkage, swelling.With respect to the dry crosslinking fiber, disclosed aqueous solution cross filament has bigger flexible and lower rigidity among the U.S.P3241552, and it is characterized in that fluid retention (FRV) height.Compare with the absorbing structure that is made by the dry crosslinking fiber, the absorbing structure that is made by aqueous solution cross filament has lower wet and dried resilience.

Be issued at 1977.7.12 among people's such as Sangenis the U.S.P4035147 and disclose a kind of method for preparing single cross filament, it be the water that contains the amount that is not enough to cause the fiber swelling, basically in the solution of non-water, the non-swelling fiber of dehydration is contacted with catalyst with crosslinking agent.Basically take place in the solution of non-water the time crosslinked when fiber is in this.Such method should be called the non-aqueous solution cross-linking method from now on; Zhi Bei fiber should be called the non-aqueous solution cross filament thus.Be disclosed in the non-aqueous solution cross filament among the U.S.P4035147, even swelling is not taking place when well known to a person skilled in the art that sweller solution deeply contacts yet.As the dry crosslinking fiber, their highly sclerosis by cross-bond, the absorbing structure that is made by it has high relatively wet and dried resilience.

It is believed that aforesaid cross filament is applicable to the application of low-density absorbent article,, also be applicable to the application of high density absorbent article, as sanitary napkin as diaper.Yet because the shortcoming and the cost of these fibers, they can not provide the enough absorbent properties that cause great business success.In addition, these fibers have higher odour nuisance and fiber brightness is lower usually.

Use formaldehyde and various formaldehyde addition product cross-linked cellulose fibres known as prior art.For example be issued to the U.S.P 3224926 of L.J.Bernardin referring to 1965.12.21.; 1966.3.22 be issued to the U.S.P3241553 of F.H.Steiger; 1976.1.13 be issued to the U.S.P3932209 of Chatterjee; 1977.7.12 invest people's such as Sangenis U.S.P4035147; With 1973.94 U.S.P3756913 that are issued to Wodka.Unfortunately, these lists of references remarkable shortcoming is the spread effect of formaldehyde vapors to eye and skin.In addition, these fibers have higher odour nuisance and fiber brightness is lower usually.Therefore the crosslinking agent that needs a kind of cellulose fibre without formaldehyde or its unstable derivative significantly.

Other list of references discloses the use of dialdehyde crosslinking agent.For example be issued to people's such as Makoui U.S.P4689118 referring to 1987.8.25; Be issued to people's such as Dean U.S.P4822453 with 1989.4.18.People's such as Dean list of references discloses the absorbing structure that contains single cross filament, and wherein crosslinking agent is selected from C ₂-C ₉Dialdehyde, preferred glutaraldehyde.These lists of references look and have overcome many shortcomings of being brought with formaldehyde and/or formaldehyde addition product.Yet the cost for preparing fiber with dialdehyde crosslinking agent such as glutaraldehyde cross-linking is too high, to such an extent as to can not bring great business success.Therefore need to seek a kind of crosslinking agent of cellulose fibre, it was both safe in utilization to people's skin, and good aesthetic (low smell, fiber brightness height) is arranged, and commercial be again feasible.

Use specific polycarboxylic acid crosslinked cellulose fibre also known as prior art.For example be issued to people's such as Herron U.S.P5137537 referring to 1992.8.11,1993.2.2 is issued to people's such as Herron U.S.P5183707 and the U.S.P5190563 that 1993.3.2 is issued to people such as Herron.People's such as Herron list of references discloses and has contained useful C ₂-C ₉The absorbing structure of polycarboxylic acid crosslinked single fiber cellulose fiber.Be different from the acetal cross-bond that forms by monobasic and dialdehyde crosslinking agent by polycarboxylic acid crosslinked dose of ester cross-bond that forms.

The absorbing structure that the fiber single by these, that ester is crosslinked makes is with respect to the structure that contains the non-crosslinked fiber, and its Wet-resilient and dried resilience improve, and wetting reactivity is improved.And preferred polycarboxylic acid crosslinked dose, promptly citric acid can low relatively price obtain in a large number, and this makes it and formaldehyde compare with the formaldehyde addition product commercial to have competitiveness.Unfortunately, preferred C ₂-C ₉The crosslinking agent citric acid when handling the white fiber cellulose fiber under the temperature that raises gradually, can cause its variable color (i.e. jaundice).In addition, the use of alpha-hydroxy carboxylic acid compounds such as citric acid also can bring offensive odour.People's such as Herron list of references does not comprise the method that reduces smell or improve fiber brightness.

Fiber and alkaline solution (for example, the aqueous solution of NaOH) and oxidative bleaching agent (for example, hydrogen peroxide) contact have now found that, by can be removed its characteristic odor and improved its brightness.Alkaline solution has improved the pH value of final fiber, preferably is increased to 5.5 to 6.5 by 4.5.It has eliminated " sootiness and burn " odor characteristics of cross filament with being used in combination of oxidative bleaching agent.When the denseness of the oxidative bleaching agent that adds is higher, the brightness of final products can be increased to 80 to 86 by 70 to 75, and can reduces smell.

An object of the present invention is to provide that polycarboxylic acid crosslinked dose of a kind of usefulness is crosslinked, that improved absorbability and aesthetic feeling, smell reduces and the preparation method of the single fiber that brightness improves.Compare with the structure that makes by the non-crosslinked fiber by the absorbing structure that polycarboxylic acid crosslinked single fiber makes, have higher Wet-resilient and higher dried resilience.

Another object of the present invention provides polycarboxylic acid crosslinked dose of a kind of usefulness single fiber crosslinked and that contact with oxidant with alkaline solution, and the absorbing structure that makes by aforesaid this fiber, it has excellent balance on the aesthetic feeling with respect to present known cross filament.

Another object of the present invention provides polycarboxylic acid crosslinked dose of single fiber crosslinked, that smell reduces and brightness improves of a kind of usefulness, and the absorbing structure that makes by aforesaid this fiber, it has excellent balance on the absorbent properties with respect to present known cross filament.

Another object of the present invention provides the preparation method single cross filament, viable commercial that a kind of smell reduces and brightness improves, and the absorbing structure that is made by aforesaid this fiber, and it can safe handling around application on human skin.

Have now found that for the structure that contains the single cross filament that scent of reduces, brightness improves, the raising of absorbing structure performance can obtain by using the single cross filament that makes by method disclosed herein.

In view of the above, the enforcement by following method prepares this fiber, and the method includes the steps of:

A., cellulose fibre is provided;

B. make this fiber and contain and be selected from C ₂-C ₉The solution contact of the crosslinking agent of polybasic carboxylic acid;

C. this fiber of mechanical separation is to being single form basically;

D. dried fibres and make it and crosslinking agent reaction when fiber is single form basically forms intrafiber crosslink connection key; With

E. by described cross filament is contacted with an alkaline solution, make the pH value of cross filament be increased at least about 5.

The single fiber cellulose fiber contacts with the crosslinking agent of capacity, in the dry fiber weight is benchmark, make effective dose, preferred about 0.1 weight % is to about 10.0 weight %, and more preferably from about 3.0 weight % are to the crosslinking agent and fiber-reactive formation fibrous inside cross-bond of about 8.0 weight %.Crosslinked single fiber cellulose fiber is contacted with the alkaline solution of capacity, and preferred about 0.07 weight % is to the alkali compounds of about 1.8 weight %, and is preferably about 5 to 7 so that the pH value of fiber is increased at least about 5, most preferably is about 5.5 to 6.5.For some application, the pH value can be increased to 10.5.This fiber also can contact with strong oxidative bleaching agent, and the amount of oxidative bleaching agent is preferably about 0.02 weight % to about 1.5 weight %.Have now found that,, can reduce the smell of fiber effectively and improve their final brightness with an alkaline solution and the oxidative bleaching agent processing fiber that combines.

Need not to be subject to theory, it is about 10.5 to it is believed that use by alkaline solution is increased to the pH value of final fiber by about 4.5, is preferably approximately 5.5 to 6.5, phenoplasts can be become the form of nonvolatile phenates.Phenates is not volatile under higher pH value.In addition, higher pH will be got rid of the possibility that forms a large amount of hydrogen sulfide.Moreover alkaline oxidiser (for example, hydrogen peroxide) it is believed that oxosugar is decomposed label such as furfural, and methyl furfural and guaiol also reduce the amount of citric anhydride.

Certainly, the alkaline solution of preferred use and the amount of oxidant will depend on used specific reagent and reaction condition, particularly air temperature and current.In an embodiment preferred, fiber solidify and wetting again after, contact with NaOH (18% technical grade), the additional proportion of NaOH is about 10 pounds to 20 pounds of the fiber that parches fully per ton.The additional proportion of hydrogen peroxide (19% technical grade) is about 4 pounds to 20 pounds of the fiber that parches fully per ton.When Wetting pump siphon again, add NaOH, just before wetting injection nozzle again, when mixture enters the fiber steam, add hydrogen peroxide.This makes cross filament contain 10% moisture based on the amount of the chemical substance of using, and its final pH value is 5.5 to 6.5.

The pH value that improves cross filament in the said method is preferably carried out simultaneously with the step that cross filament is contacted with oxidant, to simplify method of the present invention.Yet these two method steps also can carry out in proper order.For example, fiber is contacted with alkaline solution improving the pH value of fiber, and then contact with oxidant.Perhaps, cross filament is at first contacted with oxidant, and then contact with alkaline solution.Therefore, the present invention should be understood as and in cross filament, add alkaline solution and oxidant with any specific order.

Fiber is preferably crosslinked under the condition of highly pooling capital.In the most preferred embodiment, fiber is contacted with crosslinking agent in the aqueous solution, dehydration then, mechanical separation is single form extremely basically, and is crosslinked under the dry and substantially not limited then condition.Dehydration, mechanical separation and drying stage make fiber become before crosslinked and highly twist.Twisting is at least in part by due to crosslinked, but is not fully.Preferably, fiber contacts with oxidant with alkaline solution after crosslinked finishing.

The cellulose fibre of various natural origins all is applicable to the present invention.The preferred boiling fiber (digested fiber) that uses from cork, hardwood or velveteen.Also can be with by needle Rhizoma Imperatae among the present invention, bagasse is robbed hair, flax and fiber and other wooden using as raw material with cellulose fibre of coming.Can be with slurry, the form delivery of fibers of non-sheet or sheet.Preferably will be with wet cover plate, the fiber of dried cover plate or the supply of other sheet form, preferably at fiber with before crosslinking agent contacts, make it become aschistic form by machinery decomposition with these sheets.Equally, optimum fiber provides under wet or moist condition.Most preferred fiber is never dry the mistake.Under the situation of dried cover plate, advantageously before machinery decomposes that fiber is wetting, so that the destruction of fiber is reached minimum.

The specific final use that will depend on imagination in conjunction with the best fiber source of the present invention's use.Usually, the paper pulp fiber that preferably makes by the chemical pulp method.What be suitable for has full bleaching, partial bleaching and a fiber non-bleaching.Often be the paper pulp of wishing to use bleaching, in order that its splendid brightness and consumer's requirement.The preferred in the method for the invention xylon of partial bleaching at least that used.For absorption pad and other similar absorbent paper article as paper handkerchief and diaper, sanitary napkin and menopad, since its splendid absorption characteristic, the therefore preferred especially fiber that uses southerly softwood pulp.

Be applicable to that crosslinking agent of the present invention comprises aliphatic series and alicyclic C ₂-C ₉Polybasic carboxylic acid.Here employed term " C ₂-C ₉Polybasic carboxylic acid " be meant and contain two or more carboxyls (COOH), and contain the organic acid of 2 to 9 carbon atoms in the chain of the carboxyl of ining succession or the ring.Do not comprise carboxyl when determining chain or nuclear carbon atomicity.For example, 1,2, the 3-tricarballylic acid will be considered to contain the C of three carboxyls ₃Polybasic carboxylic acid.Similarly, 1,2,3, the 4-butanetetra-carboxylic acid will be considered to contain the C of four carboxyls ₄Polybasic carboxylic acid.

More particularly, be suitable among the present invention and make cellulose crosslinked dose C ₂-C ₉Polybasic carboxylic acid comprises aliphatic series and alicyclic acid, they are that olefinic is saturated or undersaturated, or have three in each molecule at least, the unsaturated acids of preferred more a plurality of carboxyls, or if each molecule when carbon-carbon double bond is present in α, the β position of one or two carboxyl has the unsaturated acids of two carboxyls.Have activity, another requirement to be when making the esterified cellulose hydroxyl, a given carboxyl in the aliphatic or alicyclic polybasic carboxylic acid must be separated by by being no less than two and no more than three carbon atom and another carboxyl.Need not to be subject to theory, can be found out significantly by these requirements, for activated carboxyl, it must form five yuan or hexa-atomic anhydride rings with the carboxyl of vicinity in the polybasic carboxylic acid molecule.When two carboxyls are separated by by a carbon-carbon double bond, or two carboxyls are when all being connected in same ring, and these two carboxyls must be to be cis-configuration mutually, if their interactional by this way words.

Contain among the aliphatic polycarboxylic acid of three or more carboxyls at each molecule, be connected in hydroxyl with respect to the α position carbon atom of carboxyl and do not disturb the crosslinked of esterification by acid and cellulose fibre.Therefore, polybasic carboxylic acid such as citric acid (being also referred to as 2-hydroxyl-1,2, the 3-tricarballylic acid) and tartaric acid monobutane diacid, the crosslinking agent that suits for the present invention.

Aliphatic and alicyclic C ₂-C ₉Polycarboxylic acid crosslinked dose also can contain aerobic or sulphur atom in the chain of the carboxyl of ining succession or ring.Therefore, polybasic carboxylic acid such as oxo two succinic acid (being also referred to as 2,2 '-oxo two (succinic acid)), thio-2 succinate and analog thereof are also included within the scope of the present invention.For purposes of the invention, oxo two succinic acid will be counted as the C that contains four carboxyls ₂-C ₉Polybasic carboxylic acid.

The example of specific polybasic carboxylic acid within the scope of the present invention comprises following: maleic acid, citraconic acid (being also referred to as citraconic acid), citric acid, itaconic acid (being also referred to as methylene-succinic acid), tricarballylic acid (are also referred to as 1,2, the 3-tricarballylic acid), trans-aconitic acid (is also referred to as anti-form-1-propylene-1,2,3 tricarboxylic acids), 1,2,3,4-butanetetra-carboxylic acid, all-cis formula-1,2,3,4-encircles penta tetrabasic carboxylic acid, mellitic acid (being also referred to as benzene hexacarboxylic acid), and oxo two succinic acid (being also referred to as 2,2 '-oxo two (succinic acid)).Above-mentioned listed concrete polybasic carboxylic acid is not to be meant to comprise all only for purposes of illustration.Importantly, crosslinking agent must with a single fiber cellulose fiber in, near at least two hydroxyl reactions on the cellulose chain of position.

Preferably, used here C ₂-C ₉Polybasic carboxylic acid contains the aliphatic saturated acid of three carboxyls for per molecule at least.One group is used for preferred polycarboxylic acid crosslinked dose of the present invention and comprises citric acid (being also referred to as 2-hydroxyl-1,2, the 3-tricarballylic acid), 1,2,3-tricarballylic acid and 1,2,3,4-butanetetra-carboxylic acid.Citric acid is particularly preferred, because it makes fiber have higher uptake and resilience, to people's skin safe and non-stimulated, and can provide stable cross-bond.And citric acid can low relatively price obtain in a large number, this make it as crosslinking agent commercial be feasible.

Be used for another group preferred cross-linking agents of the present invention and be included in the saturated C that chain that carboxyl ins succession contains at least one oxygen atom ₂-C ₉Polybasic carboxylic acid.The example of this compounds comprises oxo two succinic acid, has the tartaric acid monobutane diacid of following structural formula:

With the two succinic acid of the tartaric acid with following structural formula:

About the more detailed description of two succinic acid of tartaric acid monobutane diacid, tartaric acid and their salt, be issued to people's such as Bush U.S.P4663071 referring to 1987.5.5, it is drawn be reference here.

The technical staff in polybasic carboxylic acid field as can be seen, above-mentioned aliphatic series and alicyclic C ₂-C ₉Polycarboxylic acid crosslinked dose can exist in a variety of forms, as the form of free acid form and salt thereof.Although preferred free acid form, all these forms all within the scope of the present invention.

Single cross filament of the present invention contain effective dose, with the C of fiber with the reaction of intrafiber crosslink connection key form ₂-C ₉Polycarboxylic acid crosslinked dose.Here used " crosslinking agent of effective dose " be meant with respect to common non-crosslinked fiber, is enough to make at least one important absorbent properties of fiber self to increase and/or contains the amount of the crosslinking agent that the absorbing structure of single cross filament improves to some extent.An example of important absorbent properties is dropping liquid capacity (drip capacity), and it is to combine mensuration with the absorption of fluids capacity and the absorption of fluids speed of absorbing structure.The mensuration process of dropping liquid capacity is with auspicious stating in the content below.

Especially, weight in dried fiber is benchmark, for with contain with 1.0 weight % fiber-reactive, about to about 10.0 weight %, more preferably from about 3.0 weight % obtain quite unexpected good result to the absorption pad that the single cross filament of the crosslinking agent of about 8.0 weight % makes.Preferably, after cross-linking reaction takes place, make fiber and about 0.07 weight % alkali compounds, and about 0.02 weight % is to the strong oxidizer contact of about 1.5 weight % to about 1.8 weight %.

Preferably, crosslinking agent infiltrates through at crosslinking agent under the condition of single fiber inside configuration and contacts with fiber.This comprises the injection of the fiber of paper pulp sheet.

The applicant has now found that cross-linking reaction can practical speed be finished under without the condition of catalyst, condition is that the pH value remains on a specific scope interior (below will describe in detail).These are said different with prior art, in the prior art for making viable commercial, need specific catalyst that enough fast esterification by polycarboxylic acid crosslinked dose of fibrous cellulose and crosslinked is provided.For example be issued to people's such as Welch U.S.P4820307 referring to 1989.4.11.

Yet if need, fiber can be before crosslinked contacts with suitable catalyst.The applicant has now found that the contact method of the type of catalyst, consumption, catalyst and fiber will depend on the concrete cross-linking method of employing.These versions are auspicious stating below.

In case fiber is handled (if the words of using also have catalyst) with crosslinking agent, just cause not existing under the condition of Cheng Jian between fiber, crosslinking agent and fiber-reactive, that is to say, this moment is with respect to non-fluffy paper pulp fiber, what contact between fiber remains on lower level, and perhaps fiber is immersed in and is difficult for making Cheng Jian between fiber, particularly in the solution that hydrogen bond forms.This will cause is the formation of cross-bond of fiber internal key in essence.Under these conditions, react cross-bond between the hydroxyl that can form single cellulose chain or the cross-bond between the hydroxyl on a cellulose chain cellulose fibre, close of crosslinking agent.

Although do not point out or will limit the scope of the invention unintentionally, it is believed that polycarboxylic acid crosslinked dose carboxyl and cellulosic hydroxyl reaction forms ester bond.Ester bond it is believed that the type that provides the desirable key of stablizing cross-bond, and the formation to it under the acid reaction condition is favourable.Therefore, for purposes of the present invention, the special crosslinked condition of preferred acidic, promptly pH value scope is about 1.5 to about 5.

Before crosslinking agent and fiber-reactive, preferably, with fibre machinery be separated into the low-density single fiber form that is known as " fluffy ".Can be by well known in the art or carry out the mechanical separation of fiber by the several different methods that following content can be understood.The mechanical separation of fiber is preferably undertaken by becoming knot and the destruction of fiber being reached minimized method.Have now found that being specially adapted to one type the equipment that cellulose fibre separates is that 1976.10.26 is issued to disclosed three stage fiber separation equipments among D.R.Moore and O.A.Shields, the U.S.P3987968, this patent is drawn in this manual and is reference.The combination that the fiber separation equipment among the U.S.P3987968 that is disclosed in makes moist cellulosic pulp fibers be subjected to mechanical shock, mechanical agitation, air-flow stirring and limited amount gas drying is handled, and forms the fluffy fiber of essentially no knot.With respect to naturally occurring curling and the amount of the twist in this fiber, single fiber is given curling and the twist that its degree increases.It is believed that the curling and twist of this increase has improved the resilience of the absorbing structure that is made by final cross filament.

The method of other defibre cellulose fiber applicatory including but not limited to, handle and fiber tangentially contacted with rotating disc type refiner or wire brush with the Waring blender.Preferably, in this defibration process with the direct guide fiber of an air-flow, so that fiber separation becomes single basically form.

Do not consider the concrete machinery of used formation fluffy fiber, when fiber contains moisture at least about 20% at first, preferably contain when having an appointment 40% to about 65% moisture, preferably, fibre machinery is handled.

Also can use the machine finish of the dry fiber of the machine finish of the fiber under the high-consistency or part, purpose be except that the mechanical separation fiber the result gave curl and the twist, revest fiber certain curling and the twist.

Fiber by the present invention's preparation has rigidity and resilience, the unique combination of low smell and high brightness, these make the absorbing structure that is made by this fiber keep high-caliber absorbability, and have high-caliber resilience, and absorbing structure dry, compression is to wetting response with expansion.The crosslinking degree in having described scope, another feature of this cross filament is that its water retention of paper fibre (WRV ' s) for the chemical pulp of routine is less than about 60, more preferably about 28 to about 50, most preferably be about 30 to about 45, the smell rank of its " sootiness " and " burning " is preferably 0 to about 1 for less than 2.The feature that keeps comprises that also the level of sugar decomposition label and acid anhydrides reduces.In addition, final pH value is preferably about 5.5 to about 6.5, and brightness is greater than 80.The WRV of special fiber is the reflection of crosslinking degree.Highly cross-linked fiber as the fiber by the preparation of the cross-linking method of previously described many prior aries, has found that its WRV ' s is less than about 25, usually less than about 20.Certainly, used specific cross-linking method will influence the WRV of cross filament.Yet, anyly will cause crosslinking degree in the described scope and the method for WRV ' s, it is believed that with, and tend within the scope of the invention.Cross-linking method applicatory is included in and makes general dry crosslinking method and the non-aqueous solution cross-linking method of describing in the background technology of invention.Some preferably prepare the dry crosslinking method and the non-aqueous solution cross-linking method of single cross filament of the present invention, will be for a more detailed description below.The aqueous solution cross-linking method that solution causes fiber to become the height swelling will cause the WRV ' s of fiber to surpass about 60.These fibers do not have enough rigidity and the resilience for the object of the invention.

Specific to the dry crosslinking method, the single cross filament that smell reduces can be by following method preparation, a certain amount of cellulose fibre promptly is provided, the paper pulp sheet of fiber is contacted with the crosslinking agent of aforesaid type and consumption, with its mechanical separation, for example, the form that fiber separation is extremely single basically, with fiber drying and when fiber keeps single basically form, crosslinking agent and fiber are reacted in the presence of catalyst forming cross-bond, and cross filament and alkaline solution are contacted with oxidant with reduction smell and the brightness that improves fiber.Fiber separation step, rather than drying steps it is believed that and will give fiber extra curling.Drying subsequently is accompanied by the twisting of fiber, and Jia Nian degree improves by the curling geometry of fiber simultaneously.Here " curling " of used fiber is meant the Geometrical Bending of the fiber on the long axis direction of fiber." twisting " is meant the rotation of the fiber on the vertical cross-section of fiber major axis.Fiber in the preferred embodiment of the invention is single, and fibrous inside is cross-linked into key, and is highly twisting and curls.

Terminology used here " twisting count " is meant the quantity of the intrastitial sth. made by twisting knot that is present in certain-length.Twisting count is used to weigh the rotation degree of fiber around its major axis.Term " twist with the fingers knot " is meant around 180 ° the axial rotation basically of fiber major axis, when fiber when microscopically is used viewed in transmitted light, wherein a part of fiber (i.e. " knot ") presents dead color with respect to the fiber of remainder.Distance is corresponding to 180 ° axial rotation between knot.Those skilled in the art will appreciate that the appearance of above-mentioned sth. made by twisting knot, mainly is vision rather than physical phenomenon.Yet, twist with the fingers the degree of the direct reflection of number (being twisting count) of knot in the certain-length fiber as the fiber twisting of the physical parameter of fiber.Twisting with the fingers the outward appearance of knot and quantity, will to depend on fiber be summerwood fiber or spring wood fiber and change.Sth. made by twisting knot and total twisting count are measured by the twisting count image analysis that is described in specification test method part.The average twisting count that is used to describe fiber of the present invention is suitably measured by above-mentioned twisting count method.When to sth. made by twisting knot counting, the pars fibrosa of deepening should come with the pars fibrosa difference of twisting the obfuscation that seems owing to fiber because fiber destruction or fiber compress.

The actual twisting count of any given fiber sample will depend on the ratio of spring wood fiber and summerwood fiber and change.The twisting count of any specific spring wood or summerwood fiber also will change with the variation of fiber.Although as mentioned above, being limited to of average twisting count is suitable among definition the present invention, no matter any particular combination of spring wood fiber and summerwood fiber, these limit all suitable.That is to say that as long as meet the requirement of the qualification of other statement, any have a fiber in batch that is included in the described twisting count twisting count in limiting, all within the scope of the present invention.

In the mensuration of the twisting count of fiber sample, for reflecting the average twist level of different single fiber twist level exactly, importantly the amount of the fiber of Ce Dinging is wanted enough greatly.Suggestion is for obtaining the twisting count of representational fiber, should test 5 inches long fibers of accumulative total of the representative sample in the fiber in batch at least.

Description and mensuration to the wet fiber twisting count are similar to dried fiber twisting count, and the difference of described method only is that fiber by water-wet, was counted its twisting count according to twisting count fiber image analysis when fiber is wetting before handling.

Preferably, the average twisting count of dried fiber is at least 2.5 every millimeter sth. made by twisting knots approximately, and the average twisting count of wet fiber is at least 1.5 every millimeter sth. made by twisting knots approximately, and lacks 1.0 every millimeter sth. made by twisting at least than its dried fiber twisting count and tie.Most preferably, the average twisting count of dried fiber is at least 3.0 every millimeter sth. made by twisting knots approximately, and the average twisting count of wet fiber is at least 2.0 every millimeter sth. made by twisting knots approximately, and lacks 1.0 every millimeter sth. made by twisting at least than its dried fiber twisting count and tie.

Except that plying, it is curling that fiber of the present invention also is.Fiber crimp can be described to owing to twist together, and twisting and/or the crooked pars fibrosa that is caused shorten.For the purpose of this specification, fiber crimp should be measured in the mode of two dimension.The degree of fiber crimp is called the fiber crimp index.The fiber curl factor that the two dimension of curling is measured is by observing fiber in two dimensional surface, and the projected length of measuring fiber is as the length that surrounds the rectangular longest edge of fiber, L _R, and the physical length L of mensuration fiber _A, and calculate fiber curl factor by following equation:

(1) twist factor=(L _A/ L _R) ^-1

Measure L with fiber crimp index image analysis _RAnd L _AThis method is described in the test method part of this specification.The background information of this method is disclosed in 1979 International Paper PhysicsConference Symposium, The Harrison Hotel, Harrison Hot Spring, BritishColumbia, September 17-19,1979 (international paper physical conference seminars in 1979, the Harrison restaurant, the Harrison hot spring, Britain Colombia, 17-19 day in September, 1979), wherein have the exercise question of one piece of paper to be " Application Of Image Analysis To Pulp Fiber CharacterizationPart 1 " (the image application analysis characterizes paper pulp fiber, part 1), by B.D.Jordan and D.HPage work, 104-114 page or leaf, Canadian Pulp and Paper Association (Canadian paper pulp and paper association) (Montreal, Quebec, Canada), this specification draws the document and is reference.

Preferably, it is about 0.30 that the twist factor of fiber is at least, and more preferably is at least about 0.50.

The maintenance fiber is single form basically in dry and cross-linking process, makes fiber twist in dry run, and is cross-linked into this twisting, curling state thus.Be called at dried fibres under the condition freely basically at dried fibres under the condition that this fiber can be twisted and curl.On the other hand, dried fibres causes dry fiber to be not so good as with the like that highly twisting and curling of fiber of single form drying basically under form in blocks.The twisting and curling relative appearance of fiber that it is believed that interfibrous hydrogen bond " restriction ".

Can make fiber contact (if using catalyst) with catalyst with crosslinking agent by several different methods.In one embodiment, the fiber with paper pulp sheet form contacts with the solution that initially contains crosslinking agent and catalyst.In another embodiment, fiber contacts with the aqueous solution of crosslinking agent, and before adding catalyst it is soaked.Add catalyst subsequently.In another embodiment, crosslinking agent and catalyst are joined in the pulp material of cellulose fibre.Except that method described herein, other method is conspicuous for those skilled in the art, and they also are contained in the scope of the present invention.No matter adopt which kind of specific fiber to contact the method for (if using the words of catalyst) with catalyst with crosslinking agent, preferably, with cellulose fibre, crosslinking agent and catalyst mix and/or make it and fiber fully soaks, to guarantee they and fully the contacting and immersion of single fiber.

Can cross filament be reduced with smell by several different methods contacts with blast reagent.In one embodiment, after the discharging of pneumatic conveying drying stage, it is contacted with fiber.Fiber is dry when initial, and with after fiber contacts, the denseness of fiber is approximately 90% at chemicals.Final pH value is 5.5 to 6.5.

The applicant has now found that, remains in the following restricted portion if contain the pH value of the solution of crosslinking agent, and then cross-linking reaction can be finished under the condition of not using catalyst.Especially, in the contact process of crosslinking agent and fiber, the target pH value of part of the water-based in the cellulose fibre slurry or cross-linking agent solution should be adjusted to about 1.5 to about 5, more preferably be about 2.0 to about 3.5.Preferably, by in cross-linking agent solution, adding alkali,, regulate the pH value as NaOH.

Although as mentioned above, but can use the material of any catalytic crosslinking course usually.Catalyst applicatory comprises alkali-metal hypophosphites, alkali-metal phosphite, alkali-metal polyphosphate, alkali-metal phosphate and alkali-metal sulfate.Particularly preferred catalyst is alkali-metal hypophosphites, alkali-metal phosphate and alkali-metal sulfate.Although the applicant thinks that catalyst only plays the effect of buffer, keep the pH value in required scope, still do not know the mechanism of catalysis.Be applicable to that the more complete catalogue of this catalyst can be issued to people's such as Welch U.S.P4820307 referring to 1989.4.11, it drawn to be reference here.Selected catalyst can use separately, or combines use with one or more other catalyst.

Certainly, the amount of the preferred catalyst that uses depends on specific cross linker type and consumption, and reaction condition, particularly temperature and pH value.Usually, consider that based on the weight of the crosslinking agent that adds cellulose fibre, the amount of preferred catalyst is that about 5 weight % are to about 80 weight % from technology and economic angle.For example, as sodium hypophosphite and crosslinking agent during as citric acid, based on the amount of the citric acid that adds, the amount of preferred catalyst is about 50 weight % at the catalyst that uses.In crosslinking agent and process that fiber contacts, also need pH value with the water-based part of cellulosic fibre slurry or cross-linking agent solution to be adjusted to about 1.5 to about 5, more preferably be adjusted to about 2.0 to about 3.5.Certainly, the preferred use amount of alkaline solution and oxidant depends on used particular agent and reaction condition, particularly temperature, time and air-flow.Usually, consider that from technology and economic angle the amount of preferred alkali compounds is 0.07 weight % to 1.8 weight %, the amount of oxidant is 0.02 weight % to 1.5 weight %.Preferably, final pH value is about 5.5 to about 6.5.

Usually cellulose fibre should be dewatered, and randomly carry out drying.That can work will depend on used its fluffy device type that makes with denseness the best.In an embodiment preferred, with cellulose fibre dehydration, and preferably be dried to denseness be about 20% to about 80%.More preferably, cellulose fibre being dewatered and is dried to denseness is about 35% to about 60%.Fiber drying to these preferred range, will be helped to make fiber separation to single form, and do not cause too much formation that interrelate with high moisture content, knot and considerable damage that interrelate with low moisture content, fiber.

For example, dehydration can be by as mechanical presses, centrifugal or the air dried method of paper pulp finished.Randomly, fiber can be dried to once more denseness and be the scope of 35～60% above-mentioned denseness, but preferably, this dryly once more undertaken by air dried method well known in the art, dry condition is not need to use the high temperature drying of time expand.Temperature that this stage is too high and time expand, can cause dried fibres to denseness to surpass 60%, may will produce too much fiber destruction in the fiber separation stage subsequently thus.After the dehydration, as mentioned above fibre machinery is separated.

Then the fiber that separates being dried to denseness by flash drying method well known in the art is 60% to 100%.Because moisture is removed from fiber, this stage gives the extra twist of fiber and curls.Although it is different by the amount of moisture that this extra drying steps is removed, but it is believed that in 60% to 100% consistency range flash drying fiber to higher consistency ratio flash drying fiber to lower denseness will make fiber have the higher levels of twist and curl.In an embodiment preferred, be about 90% to 95% with fiber drying to denseness.It is believed that to need not higher flash drying temperature and reach the required duration of 100% denseness that the flash drying of this degree makes fiber have the twist of aequum and curls.With the denseness of the higher part in fiber flash drying to 60%～100% scope, as 90%～95%, also can reduce cure stage after the flash drying the dry amount that must finish.

Fiber with flash drying is heated to suitable temperature and continues one effective period then, so that crosslinking agent solidifies, promptly reacts with cellulose fibre.Crosslinked speed and degree depend on the degree of drying of fiber, temperature, pH value, the type of catalyst and crosslinking agent and consumption, and used heating and/or the method for dried fibres during crosslinked carrying out.For the certain fiber of original water content, than its drying/heating in static baking oven, the cross-linked speed of fiber wants fast under specified temp with continuous blowing air drying.One of skill in the art will appreciate that curing, have a large amount of temperature-time relationships for crosslinking agent.Less than about 10% fiber, baking temperature is about 145 ℃ to about 165 ℃ under the still air condition, about 30 minutes to 60 minutes of drying time, will provide acceptable curing efficiency usually for moisture.Those skilled in the art will recognize that equally high temperature and reinforcement cross-ventilation can reduce and solidify the required time.Therefore, less than about 10% fiber, in the baking oven of blowing air, about 170 ℃ to about 190 ℃ of baking temperature, will provide acceptable curing efficiency usually equally at about 2 minutes to 20 minutes of drying time for moisture.Solidification temperature should remain on less than about 225 ℃, preferably less than about 200 ℃, because fiber is exposed to and can causes deepening under such high temperature or to other destruction of fiber.

Need not to be limited by theory, it is believed that cellulose fibre and C ₂-C ₉Polycarboxylic acid crosslinked dose chemical reaction just can begin to carry out when the mixture of these raw materials heats in curing oven.In cure stage, C ₂-C ₉Polycarboxylic acid crosslinked dose and cellulosic intermolecular formation ester cross-bond.The crosslinked of these ester bond forms is variable under the influence of heat, because ester exchange reaction can take place the not esterified hydroxyl on the cellulose fibre of ester group and vicinity.And it is believed that betiding initial ester bond forms ester exchange process afterwards, to such an extent as to cause these fibers to be compared, have the absorbent properties of raising with solidifying the also nonevent fiber of insufficient ester exchange.

After the cross-linking step, fiber is carried out post processing to reduce smell and to improve brightness.Fiber contacts with oxidant with an alkaline solution.Alkaline solution contains an a kind of aqueous medium and an alkali compounds.Preferred alkali compounds is selected from NaOH, clorox, sodium hydrogensulfite, ammonium hydroxide and their mixture, and wherein NaOH is most preferred.Preferably, the pH value of alkaline solution is greater than about 9.

Preferably, oxidative bleaching agent is selected from hydrogen peroxide, sodium peroxide, peracetic acid, chlorine dioxide, clorox, hydrogen chloride and composition thereof, and wherein hydrogen peroxide is most preferred.But the also chemical substance that can use other to use as bleaching agent.

Preferably, the pH value of fiber is improved and be maintained at about 5.5 to about 6.5 level.Fiber can not be introduced these reagent wherein before crosslinked, and preferably, it is very important that the final pH value is lower than 7.0.Fiber is simply handled to the air-flow that contains fiber by spraying NaOH and hydrogen peroxide, can be reduced smell to zero and brightness is increased to 80-85 by about 75.The fiber that beginning contacts with these reagent parch when preferably it is initial, and preferably, its total moisture content keeps below 10%.It is believed that this method has embodied the optimal way of the cross filament that the preparation smell reduces, because it has avoided the inconvenience in the expensive and extra processing that bleaching and washing brought.In addition, have now found that common multistep bleaching and washing after crosslinked can bring ideal results.These comprise DEP or DEH step, and wherein D is a chlorine dioxide, and E is the caustic alkali extraction, and P is a peroxide, and H is a clorox.Preferably, the step after crosslinked is alkali treatment, but final pH value should be adjusted to and is lower than 7.

Crosslinkedly will when being in drying in fact, fiber (moisture is lower than about 5%) reach top.Owing to there is not water, fiber is crosslinked when the state of non-swelling, shrinkage basically.Therefore, with respect to the present invention's scope applicatory, has to their features low fluid retention (FRV).FRV is meant the amount based on dried fiber, and one is soaked and the centrifugal then fiber sample of removing interfibrous fluid, and institute keeps the amount of the fluid of absorption.(will be further described below the definition of FRV and the method for measuring FRV.) amount of the absorbable fluid of cross filament depends on their swelling abilities when saturated, perhaps in other words, inside diameter when they are swelling at utmost or volume.This equally also depends on crosslinked degree.For given fiber and processing procedure, along with the increase of fibrous inside crosslinking degree, the FRV of fiber will reduce.Therefore, the FRV value of fiber from structure explanation fiber the physical state when saturated.Unless add explanation in addition, FRV data described here should occur with the form of the water retention (WRV) of fiber.Other fluid as salt solution and synthetic urine, advantageously, also can be used as the fluid media (medium) of analyzing usefulness.Usually, for mainly depending on drying,, crosslinking agent and crosslinked degree will be depended on mainly as the FRV of the crosslinked special fiber of method of the present invention by solidifying.By WRV ' s with the cross filament that obtains applicable to the dry crosslinking method of dosage of crosslinking agent of the present invention, be generally less than about 60, greater than about 28,, more preferably be about 30 to about 45 preferably less than about 50.Weight in dried fiber is benchmark, has found to have southern softwood kraft (SSK) fiber of about 1.0 weight % to the bleaching of the citric acid of the participation reaction of about 10.0 weight %, and its WRV ' s is respectively about 28 to about 40.Have now found that the degree of bleaching and the enforcement of crosslinked after bleaching step will influence WRV.SSK fiber by the known cross-linking method preparation of many prior aries has greater than crosslinking degree described here, and its WRV ' s is less than about 25.Have now found that this fiber, as previously mentioned, its exceedingly hard and its absorptive capacity is less than fiber of the present invention.

Prepare by the dry crosslinking method in the method for single cross filament at another, the solution that cellulose fibre and contains aforesaid crosslinking agent contacts.Though with before crosslinking agent contacts or after, fiber all provides with the form of sheet.Make its drying at fiber during with the form of sheet, and preferably make it crosslinked by fiber being heated to about 120 ℃ to about 160 ℃.After crosslinked, with fibre machinery be separated into single basically form.Preferably, this process is undertaken by using for example processing of the described fiber fluffy equipment of U.S.P3987968, and perhaps also other method of available defibre well known in the art is carried out.Will be according to the single cross filament of this sheet cross-linking method preparation, crosslinking agent with capacity is handled, molal quantity in the cellulose anhydroglucose is benchmark and measures after fiber separation, make the crosslinking agent of effective dose, preferably about 1.0 weight % are to the crosslinking agent of about 10.0 weight %, with the form reaction of fiber with intrafiber crosslink connection key.Making its dry and another crosslinked effect during with the form of sheet at fiber is that interfibrous combination has limited with the twisting of the fiber that raising brought of degree of drying and curling.With dry under non-limited condition basically according to fiber, and the single cross filament for preparing with twisting, the curling crosslinked method of configuration is subsequently compared, the absorbing structure that contains the fiber of the non-relatively twisting that makes by above-mentioned sheet solidification method, will have lower Wet-resilient and to wetting than low-response.

Also can consider between drying and cross-linking step fibre machinery is separated into single basically form.That is to say, fiber is contacted with crosslinking agent, and drying when it is the form of sheet subsequently.Fiber is single form and can helps the crosslinked of fibrous inside before crosslinked.This cross-linking method that replaces, and other the whole bag of tricks apparent to those skilled in the art include within the scope of the invention.

Another is a non-aqueous solution curing cross-linked method applicable to cross-linking method of the present invention.Be applicable to that the fiber of the same-type of dry crosslinking method also can be used for the preparation of non-aqueous solution cross filament.With fiber with the crosslinking agent of capacity, and if need and suitable catalyst treatment, make effective dose crosslinking agent subsequently with fiber-reactive.The amount of crosslinking agent that uses and catalyst (if words of using) will depend on for example denseness, temperature, the water content in the crosslinker solution, fiber, the type of crosslinking agent, the diluent in the crosslinker solution and required reaction conditions such as crosslinked amount.When fiber is immersed in the nonaqueous in fact crosslinker solution, make crosslinking agent and fiber-reactive.Nonaqueous crosslinker solution contain a kind of non-water, with the mixable polarity diluent of water, for example, but be not limited to acetate, propionic acid or acetone.Crosslinker solution also can contain limited amount water or other fiber swelling liquid, but preferably, the quantity not sufficient of water is to cause any substantial fiber swelling.The applicable crosslinker solution system of making crosslinking medium comprises that those are issued to S.Sangenis, G.Guiroy, and and J.Quere, disclosed content among the U.S.P4035147 of 1977.7.12 is drawn it reference of making this specification here.

Preferably, prepare cross filament of the present invention according to foregoing dry crosslinking method.Cross filament of the present invention can be directly used in the absorbent core of making air lay.In addition, because their hardness and rebound characteristics, this cross filament also can wet method be made incompressible, low-density sheet, further mechanical treatment after the drying, and this sheet can directly be used as absorbent core.This cross filament also can be made the sale of compressed paper lodicule by wet-laying, or is transported to place far away.

With respect to the paper pulp sheet that is made by common non-crosslinked cellulose fibre, the paper pulp sheet that is made by cross filament of the present invention more is difficult to be compressed to common paper pulp sheet density.Therefore, cross filament and for example those non-crosslinked fibers that are generally used for making absorbent core need be combined.Based on the gross dry weight amount of sheet, contain the paper pulp sheet of the cross filament of sclerosis, preferably contain 5% to about 90% the non-crosslinked cellulose fibre of having an appointment, and mix mutually with single cross filament.The particularly preferred gross dry weight amount that is based on sheet comprises about 5% to about 30% highly refined non-crosslinked cellulose fibre.These highly refined fibers by refining or pull an oar to freedom for less than about 300 milliliters of CSF, preferably less than 100 milliliters of CSF.Preferably, the non-crosslinked fiber mixes mutually with the water paste of single cross filament.This mixture can be made fiber separation that is used for subsequently and the paper pulp sheet that forms the multiviscosisty of absorption pad then.The adding of non-crosslinked fiber makes the paper pulp sheet be easy to be compressed into the form of multiviscosisty, and simultaneously the absorbability of the absorption pad that forms is subsequently only brought very little loss.In addition, the non-crosslinked fiber also can improve the paper pulp sheet and by the TENSILE STRENGTH of paper pulp sheet or the absorption pad that directly made by crosslinked and the mixture non-crosslinked fiber.No matter be at first to make the paper pulp sheet with the mixture non-crosslinked fiber, and then form absorption pad with crosslinked, still directly form absorption pad, the paper pulp sheet all can be that the air lay method forms or wet into the formation of net method.

By single cross filament or also contain sheet or the net that the mixture of non-crosslinked fiber makes, preferably, it is quantitatively less than about 800 gram/rice ², density is less than about 0.60 gram per centimeter ³Though non-being meant to limits the scope of the invention, quantitatively be 300 gram/rice ²To about 600 gram/rice ², and density is 0.07 gram per centimeter ³To about 0.30 gram per centimeter ³The wet-laying sheet, especially preferably with it directly as the absorbent core of disposable, as diaper, stopper and other sanpro.It is believed that quantitatively and structure that density is higher than these levels be suitable for most subsequently pulverizing with the air lay method or wet into the net method and make and more be applicable to the low-density that absorbs application and quantitative structure.And this high structure quantitative and density also shows high absorbability and the response to wetting.Other purposes of fiber of the present invention comprises the low-density tissue paper of density less than about 0.03 grams per milliliter.

If need, also can further handle cross filament to remove excessive, unreacted crosslinking agent.A series of processing modes that excessive crosslinking agent can be successfully removed in discovery sequentially comprise, the washing cross filament, fiber is immersed in one section reasonable time in the aqueous solution, fiber is screened, dehydration, for example reach about 40% to about 80%, as previously mentioned the dehydration fiber is carried out mechanical separation, and fiber is carried out pneumatic conveying drying by centrifugal its denseness that makes.If need, can in wash solution, add the acidic materials of capacity, with the pH value of maintenance wash solution less than about 7.Need not to be subject to theory, it is believed that ester crosslinked under alkali condition, be unsettled, the pH value when keeping carrying out washing treatment can prevent the Back Up that established ester is crosslinked in acid range.Acidity can be introduced by inorganic acid such as sulfuric acid, or by acid bleaching chemical substance such as chlorine dioxide and sodium hydrogensulfite (also can be added into to improve the brightness of cross filament) introducing.Have now found that this method can be reduced to the content of remaining free cross-linker about 0.01% to about 0.15%.

Cross filament described here is applicable to many absorbent articles, includes but not limited to the tissue paper sheet, disposable diaper, and sanpro, sanitary napkin, stopper, and bandage, wherein said each goods all have the absorbing structure that contains single cross filament described here.For example, the top flat that the disposable diaper of special conception or similar articles have liquid permeable, the egative film of the liquid impermeable that links to each other with top flat, and the absorbing structure that contains single cross filament.These goods are disclosed among the U.S.P3860003 that 1975.1.14 is issued to Kenneth B.Buell, it are drawn the reference for this specification here.Cross filament described here also is applicable to the goods of preparation as filter medium.

Usually, the absorbent core of diaper and sanitary napkin is made by unsclerotized, non-crosslinked cellulose fibre, and wherein the dry density of absorbent core is about 0.06 gram per centimeter ³To about 0.12 gram per centimeter ³When wetting, the volume of absorbent core reduces usually.

Have now found that, with respect to the suitable absorbent core of density that makes by common non-crosslinked fiber or the known cross filament of prior art, cross filament of the present invention can be used for preparing and has the absorbent core of high fluid absorbent properties in fact, and the absorption of fluids performance includes but not limited to absorptive capacity and capillary absorption rate.And these improved absorbent properties can obtain with the Wet-resilient that improves.Basically keep when wetting constant volume, density is about 0.05 gram per centimeter ³To about 0.15 gram per centimeter ³Absorbent core, be benchmark with the molal quantity of dry cellulosic anhydroglucose, especially preferably using the degree of cross linking is the cross filaments of about 1.0 weight % to about 10.0 weight % crosslinking agents.The absorbent core that is made by such fiber has the combination of desirable structural integrity, i.e. resistance to compression and Wet-resilient.Term among the present invention " Wet-resilient " is meant wet pad in the effect of being under pressure and after pressure discharges, the ability of rebounding to its original shape and volume.Compare with the core that cross filament by untreated fiber and prior art makes, the absorbent core that is made by fiber of the present invention is after wet pressing power is removed, and its volume will return to more a high proportion of its initial volume in fact.

In another preferred embodiment, single cross filament be made into or air lay or wet (subsequent drying) into the net, be compressed into the absorbent core of dry density less than the balance wet density of pad.The balance wet density is to be benchmark in dried fiber, when the density of the pad of pad during fully by saturated with fluid.When fiber is made into dry density less than the absorbent core of balance wet density, wetting when saturated, absorbent core with shrinkage to the balance wet density.Perhaps, when fiber is made into dry density greater than the absorbent core of balance wet density, when saturated, absorbent core will be expanded to the balance wet density wetting.The balance wet density of the pad that is made by fiber of the present invention is in fact less than the pad that is made by common fluffy fiber.Fiber of the present invention can be compressed into density greater than the balance wet density, to form when wetting with the shim liner that expands, absorptive capacity can be increased to the degree that is obviously obtained like this greater than the non-crosslinked fiber.

In another preferred embodiment, be benchmark in the weight of dried fiber, crosslinking agent is the cross filaments of about 3.0 weight % to about 8.0 weight, can obtain higher absorbent properties, Wet-resilient and to wetting response.Preferably, such fiber is made into the absorbent core of dry density greater than their balance wet density.Preferably, to be pressed into density be about 0.12 gram per centimeter to absorbent core ³To about 0.60 gram per centimeter ³, wherein Dui Ying balance wet density is less than the density of doing compression pad.Equally preferably, to be pressed into density be about 0.12 gram per centimeter to absorbent core ³To about 0.40 gram per centimeter ³, wherein Dui Ying balance wet density is about 0.08 gram per centimeter ³Extremely about 0.12 fills/centimetre ³, less than the density of doing compressed core.Yet, will be appreciated that the absorbing structure in the higher density scope can be made by the higher cross filament of the degree of cross linking, can make the same by the lower cross filament of the degree of cross linking with more low-density absorbing structure.With respect to the single cross filament of prior art, all these structures all have improved performance.

Although the narration of front comprises the preferred embodiment of higher and more low-density absorbing structure, but will be appreciated that, the absorbing structure density between the described here scope and the various combinations of cross-linked dosage, with respect to the cross filament of common cellulose fiber peacekeeping prior art, all will provide splendid absorption characteristic and absorbing structure globality.These embodiments will comprise within the scope of the invention.

Measure the method for fluid retention

Can use following method to measure the water retention of cellulose fibre.

Under the room temperature, about 0.3 gram to about 0.4 fiber sample that restrains is dipped in the lidded container that fills about 100 ml distilled waters or deionized water about 15 to about 20 hours.The fiber collecting that will soak and is gone up its 60 mesh sieves bottom that is transferred to centrifuge tube in the 80 order steel crates about 1.5 inches, that supported in a filter.This pipe plastic covers, and sample is carried out 19 to 21 minutes centrifugal with the relative centrifugal force(RCF) of 1500 to 1700 gravity.Then centrifugal fiber is shifted out from basket and weigh.The fiber of weighing is dried to constant weight under 105 ℃, and weighs once more.Water retention calculated as described below: $\left(1\right)\mathrm{WRV}=\frac{(W-D)}{D}\×100$

Wherein, the weight in wet base of W=centrifugal fiber;

The dry weight of D=fiber;

The weight of the water that W-D=absorbs.

Drip the assay method of capacity

Available following method is measured the capacity that drips of absorbent core.Dripping capacity is to measure as the absorptive capacity of core and the combination of absorption rate.

4 inches * 4 inches absorbent patch of one heavily about 7.5 grams is placed on the screen cloth.Speed with 8 milliliters/second drips synthetic urine to the central authorities of pad.When first synthetic urine from the bottom of pad or the next door just stop to drip synthetic urine when spilling.Dripping capacity is to calculate like this, promptly synthetic urine introduce before the pad and weight difference afterwards divided by the weight of the fiber that parches meter.

Wet compressible assay method

Can use following method to measure the wet compressibility of absorbing structure.Wet compressibility can be used to weigh moisture-resistant compressibility, the globality of wet structure and the Wet-resilient of absorbent core.

Prepare one 4 inches * 4 inches, heavily about 7.5 pads that restrain, measure its thickness and calculate its density.Make the synthetic urine of this pad carrying 10 times or its saturation point to its dry weight, which is littler promptly to which kind of degree.Apply 0.1 pound/square inch compressive load to this pad.Measure the thickness of pad after about 60 seconds, internal gasket reaches balance during this period of time.Compressive load is increased to 1.1 pounds/square inch then, make pad reach balance and measure its thickness.To compress subsequently and carry again that lotus is decreased to 0.1 pound/square inch, and make pad reach balance and measure its thickness once more.In 0.1 pound of/square inch initial load, during 0.1 pound of/square inch load of 1.1 pounds of/square inch load and the second time, calculate the density of pad, be called 0.1PSIR (PSI (pound/square inch) resilience) load.Determine the voidage of each compressive load then, with centimetre ³/ gram meter.Voidage is (0.95 centimetre of the volume that the inverse of the wet density of pad deducts fiber ³/ gram).0.1 the voidage of pound/square inch and 1.1 pounds/square inch can be used for illustrating the globality of moisture-resistant compressibility and wet structure.For general initial pad density, higher voidage represents that moisture-resistant compressibility globality bigger and wet structure is higher.0.1 the difference of the voidage of pound/square inch and 0.1PSIR can be used for the Wet-resilient of comparison absorbent patch.0.1 the difference of the voidage of pound/square inch and 0.1PSIR is less, represents higher Wet-resilient.

Similarly, find preceding dried pad of compression and the difference of saturated pad on thickness, can be used for representing that pad is to wetting response.

Do compressible assay method

Can use following method to measure the dried compressibility of absorbent core.Dried compressibility can be used to weigh the dried resilience of absorbent core.

Prepare one 4 inches * 4 inches, the pad of air lays of heavily about 7.5 grams, and to be compressed to pressure by hydraulic pressure pressure under dry state be 5500 pounds/inch ²This pad is turned and repeats above-mentioned compression.Compression uses the no-load slide calliper rule to measure the thickness of pad before and afterwards.Calculate before the compression then and density afterwards, count quality/(area * thickness).Before the compression and the bigger expression of difference of density afterwards to do resilience lower.

C with the cellulose fibre reaction ₂-C ₉The assay method of the amount of polybasic carboxylic acid

Many Cs crosslinked with cellulose fibre that are suitable for measuring are arranged ₂-C ₉The quantitative analysis method of polybasic carboxylic acid.Can use any suitable method.In an embodiment of the present invention, join C key, preferred for measuring to form intrafiber crosslink with single cross-linked cellulose fibres component reaction ₂-C ₉The amount of polybasic carboxylic acid (being citric acid) can be used following method.At first, with the cross filament sample with the hot wash of capacity to remove any unreacted cross-linking chemistry material or catalyst.Then, with fiber drying to equilibrium moisture content.

Basically measure the carboxyl-content of single cross filament then by T.A.P.P.I.Method T 237 OS-77.Then by the carboxyl-content calculating C of following formula by fiber ₂-C ₉The crosslinked amount of polybasic carboxylic acid:

The carboxyl-content of C=cross filament wherein, milliequivalent/kilogram

The carboxyl-content of the paper pulp fiber that 30=is uncrosslinked, milliequivalent/kilogram

Draw being assumed to that following formula does:

1. the hydroxyl reaction on two in three carboxyls of citric acid and the cellulose forms cross-bond, and therefore a remaining carboxyl can freely be measured by the carboxyl test.

2. the carboxyl-content of uncrosslinked paper pulp fiber is 30 milliequivalent/kilograms.

3. in cross-linking process, do not produce new carboxyl on the cellulose.

The assay method of twisting count

Can use following method to measure the twisting count of the fiber of analyzing in this specification.

Dried fiber is placed on the micro slide that scribbles the impregnation oils film, cover with cover slip then.The effect of impregnation oils is to make fiber transparent, does not cause swelling, and determines to twist with the fingers knot (will narrate below) thus.By the fibre stuff of toppling over low denseness wet fiber is placed on the slide glass, then slide glass is covered with cover slip.Water makes fiber transparent, easily determines to twist with the fingers knot thus.

Use comprises computer-controlled microscope, video cameras, video screen and is furnished with can be by Cambridge Instruments Limited (Cambridge, England; Buffalo, New York) image analyzers of the computer of the QUIPS software that obtains is measured twisting count.

Under 200 times of amplifications, be determined at the total length of the fiber in the specific slide regional extent with image analyzers.By the operator to twisting with the fingers knot and determine and counting.This process of continuing is measured the length of fiber and is carried out mark to twisting with the fingers knot, up to the fiber total length of having analyzed 1270 mils.By these data with total sth. made by twisting footing of mark divided by total fibre length, calculate every millimeter sth. made by twisting footing order.

The assay method of twist factor

Can use following method to measure the crimp index of fiber.

Dried fiber is placed on the microscopical micro slide.Cover slip is placed on the fiber, and apply glue in edge.Measure the physical length LA of fiber and maximal projection length L R (equaling to surround the length of the rectangular longest edge of fiber) with the image analyzers of the microscope that comprises software control, video cameras, imaging monitoring device and computer.Used software is with described the same in above-mentioned twisting count image analysing computer method part.

In case draw LA and LR, promptly calculate twist factor by the equation (1) shown in top.To calculate the twist factor of each fiber sample with at least 250 single fibers, get its mean value then to determine the average twist factor of sample.Remove the fiber of LA in the calculating less than 0.25mm.

The assay method of odor compound

Can use following method to measure the odor compound content of cross filament.

Be suspended in 40 ml waters about 1 gram to the material samples of 2 grams and with its homogenizing.Press solidly body with glass bar when removing water by decant.Water is adjusted to the pH value is 4-4.3, and extract with 3-4 milliliter pentane, or by little liquid/liquid extractor extraction.

With being furnished with syringe/grabber, PID/ sucks part and mass spectrometric PE 3920 gas chromatograph analytic samples.Use long 60 meters in the analysis, internal diameter is 0.32 millimeter Restex R _Tx-1 methyl silicone post and 1 μ m film.Temperature program(me) is provided with as follows: 50 ℃ of following isothermals 4 minutes, 8 ℃/minute to 280 ℃, isothermal 16 minutes.

So obtained the chromatogram on the liquid level, and can measure the content of phenolic resins and glycolytic label.

The assay method of the smell of cross filament

Agency (proctor) (being preferably the sense of smell specialty) will fasten each bowl cover and give cup to make to go up label and prepare sample then by putting into each sample of appropriate amount in 6 ounces of lilium dixie cups.When the agency will assess sample, lid is removed, add 10 milliliters cold running water, then the lid on the cup is put back to.At least will be before the assessment sample through 2 minutes, but can not be above 15 minutes.Contain the sample sets of three cups for each, panel will at first take away the lid on the specimen cup of the standard of being confirmed as, and hear its smell.Lid should be put back on the cup then.Ensuing program is to hear the smell of remaining each sample.Panel identifies sample, on table of grading to its label, and the grade that core surely can the comprehensive smell of representative sample.This assessment can only be undertaken by those titular people.

Measure the method for brightness

Can use following method to measure brightness degree: with the Technidyne TB-1 luminance meter of standard.Use the method for industrial standard to prepare the pad of one 4 inches * 4 inches air lay.Measure the brightness of fiber then at the top in sample central authorities.

Measure the method for pH value

Can use following method to measure the pH value of final fiber: in 100 ml waters, to add 1 gram cross filament.This sample was stirred 60 minutes and write down its pH value.

Following embodiment will specify enforcement of the present invention, but will therefore limit the present invention unintentionally.

Example I

Use citric acid as crosslinking agent, reduce smell and improve brightness, be equipped with the single cross filament that smell reduces by the dry crosslinking legal system with NaOH and hydrogen peroxide.That smell reduces, as follows with the crosslinked fiber preparation method of citric acid:

1. for each sample, provide 1735 grams dry cross, southern softwood kraft slurry (SSK) with sheet form.The moisture content of fiber is about 7% (being equivalent to 93% denseness).

2. paper pulp sheet and 8% citric acid are contacted with 1% sodium hypophosphite.With NaOH the pH value is adjusted to 2.5.The paper pulp sheet of gained and the denseness of chemical substance are 60%.

3. then, with Sprout-Waldron 12 " disc type refiner (model 105-A) defibre, the fiber that the gap of plate is set to obtain is essentially single, but the amount of fiber destruction is minimum.When single fiber leaves refiner, with the hot-air of two vertical tubes they are carried out flash drying, with the twist that fiber is provided with curl.Leave have an appointment 10% moisture and performed crosslinked preparation of these Guan Shihan at fiber.If the moisture of fiber is greater than about 10% when leaving the flash drying pipe, then fiber used chamber warm air drying is about 10% until its moisture.

4. be nearly dry fiber then and be placed on the pallet, and (it depends on the consumption of citric acid in the practical operation, the degree of drying of fiber etc.) solidifies a period of time in the pneumatic conveying drying baking oven at a certain temperature.In this embodiment, sample solidified about 5 minutes down at 330 ℃.In baking oven, during this period of time will finish crosslinked.

Then with crosslinked single fiber with contain 0.25% NaOH and 0.13% hydrogen peroxide, and the aqueous solution of good mixing contact.The gained fiber contains 10% moisture.

6. smell is zero, and the final pH value is 6.0, and gained brightness is 84.This material has the sugar decomposition labelled content (5-7x) and the citric anhydride content (2-3x) of reduction.

In the dry fiber weight is benchmark, and the WRV of the single cross-linked cellulose fibres of gained is 37.6, and contain 3.5 weight %, with the citric acid of fiber with the reaction of the form of interior fiber cross-bond.Final smell is zero, and the brightness of gained is 84, and final pH value is 6.2.

Importantly, compare with the known cross filament of prior art with common non-crosslinked fiber, the smell of the single cross filament of gained reduces, and brightness improves, and wetting response is improved, and can be used in around the human body skin safely.

Example II

Use citric acid as crosslinking agent, reduce smell and improve brightness, be equipped with the single cross filament that smell reduces by the dry crosslinking legal system with NaOH and hydrogen peroxide.That smell reduces, as follows with the crosslinked fiber preparation method of citric acid:

1. for each sample, provide 1735 grams dry cross, southern softwood kraft slurry (SSK) with sheet form.The moisture content of fiber is about 7% (being equivalent to 93% denseness).

2. paper pulp sheet and 8% citric acid are contacted with 1% sodium hypophosphite.With NaOH the pH value is adjusted to 2.5.The paper pulp sheet of gained and the denseness of chemical substance are 60%.

3. then, with Sprout-Waldron 12 " disc type refiner (model 105-A) defibre, the fiber that the gap of plate is set to obtain is essentially single, but the amount of fiber destruction is minimum.When single fiber leaves refiner, with the hot-air of two vertical tubes they are carried out idle rapid drying, with the twist that fiber is provided with curl.Leave have an appointment 10% moisture and performed crosslinked preparation of these Guan Shihan at fiber.If the moisture of fiber is greater than about 10% when leaving the flash drying pipe, then fiber used chamber warm air drying is about 10% until its moisture.

4. be nearly dry fiber then and be placed on the pallet, and (it depends on the consumption of citric acid in the practical operation, the degree of drying of fiber etc.) solidifies a period of time in the pneumatic conveying drying baking oven at a certain temperature.In this embodiment, sample solidified about 5 minutes down at 330 ℃.In baking oven, in during this period of time, will finish crosslinked.

5. then crosslinked single fiber is contacted with the aqueous solution that contains 0.09 weight % NaOH and 0.02% hydrogen peroxide.The gained fiber contains 10% moisture.

In the dry fiber weight is benchmark, and the WRV of the single cross-linked cellulose fibres of gained is 37.6, and contain 3.5 weight %, with the citric acid of fiber with the form reaction of intrafiber crosslink connection key.Final smell is zero, and the brightness of gained is 84, and final pH value is 6.2.

Importantly, compare with the known cross filament of prior art with common non-crosslinked fiber, the smell of the single cross filament of gained reduces, and brightness improves, and wetting response is improved, and can be used in around the human body skin safely.

EXAMPLE III

Use citric acid as crosslinking agent, reduce smell and improve brightness, be equipped with the single cross filament that smell reduces by the dry crosslinking legal system with NaOH and hydrogen peroxide.That smell reduces, as follows with the crosslinked fiber preparation method of citric acid:

1. for each sample, provide 1735 grams dry cross, southern softwood kraft slurry (SSK) with sheet form.The moisture content of fiber is about 7% (being equivalent to 93% denseness).

2. paper pulp sheet and 8% citric acid are contacted with 1% sodium hypophosphite.With NaOH the pH value is adjusted to 2.5.The paper pulp sheet of gained and the denseness of chemical substance are 60%.

3. then, with Sprout-Waldron 12 " disc type refiner (model 105-A) defibre, the fiber that the gap of plate is set to obtain is essentially single, but the amount of fiber destruction is minimum.When single fiber leaves refiner, with the hot-air of two vertical tubes they are carried out flash drying, with the twist that fiber is provided with curl.Leave have an appointment 10% moisture and performed crosslinked preparation of these Guan Shihan at fiber.If the moisture of fiber is greater than about 10% when leaving idle rapid drying tube, then fiber used chamber warm air drying is about 10% until its moisture.

4. be nearly dry fiber then and be placed on the pallet, and (it depends on the consumption of citric acid in the practical operation, the degree of drying of fiber etc.) solidifies a period of time in the pneumatic conveying drying baking oven at a certain temperature.In this embodiment, sample solidified about 5 minutes down at 330 ℃.In baking oven, in during this period of time, will finish crosslinked.

Then with crosslinked single fiber with contain the aqueous solution of 0.16% NaOH and contact with 0.1% hydrogen peroxide.The gained fiber contains 10% moisture.

In the dry fiber weight is benchmark, and the WRV of the single cross-linked cellulose fibres of gained is 37.6, and contain 3.5 weight %, with the citric acid of fiber with the form reaction of intrafiber crosslink connection key.Final smell is zero, and the brightness of gained is 82, and final pH value is 6.4.

Importantly, compare with the known cross filament of prior art with common non-crosslinked fiber, the smell of the single cross filament of gained reduces, and brightness improves, and wetting response is improved, and can be used in around the human body skin safely.

Claims (10)

1. method for preparing smell single fiber cellulose fiber that reduce, polycarboxylic acid crosslinked, the feature of this method is that it comprises following steps:

A., cellulose fibre is provided;

B. make this fiber and the C that contains effective dose ₂-C ₉Polycarboxylic acid crosslinked dose solution contact, wherein said C ₂-C ₉Polycarboxylic acid crosslinked dose is selected from:

(i) olefinic is saturated or unsaturated, contains the aliphatic series and the alicyclic C of at least three carboxyls in per molecule ₂-C ₉Polybasic carboxylic acid; With

(ii) contain two carboxyls in the per molecule, and contain the α that is positioned at one or two carboxyl, the aliphatic series and the alicyclic C of a carbon-carbon double bond on the β position ₂-C ₉Polybasic carboxylic acid,

Wherein at described C ₂-C ₉In polycarboxylic acid crosslinked dose, a carboxyl and another carboxyl by or two or three carbon atoms separate,

C. this fiber of mechanical separation is to being single form basically;

D. dry described fiber also makes it and the crosslinking agent reaction when this fiber is single form basically, form intrafiber crosslink connection key; With

E. by described cross filament is contacted with an alkaline solution, make the pH value of cross filament be increased at least about 5, preferred 5.5 to 6.5, wherein preferably, the pH value of this alkaline solution is greater than 9.

2. the process of claim 1 wherein that pH value with cross filament is increased to is at least 5 step (e), also comprises further described cross filament is contacted with an oxidative bleaching agent.

3. claim 1 or 2 method, wherein this alkaline solution contains an aqueous medium and and is selected from NaOH, clorox, sodium hydrogensulfite, ammonium hydroxide and their mixture, the preferably alkali compounds of NaOH.

4 claims 2 or 3 method, wherein oxidative bleaching agent is selected from hydrogen peroxide, sodium peroxide, peracetic acid, chlorine dioxide, clorox, hydrogen chloride and composition thereof, preferably hydrogen peroxide.

5. each method in the claim 1 to 4, wherein the described cellulose fibre in the step (a) is at least by partial bleaching.

6. each method in the claim 1 to 5, wherein based on the dry fiber weight of cellulose fibre, 1.0 weight % to 10.0 weight %, crosslinking agent and the described fiber-reactive of preferred 3.0 weight % to 8.0 weight % form described intrafiber crosslink connection key.

7. each method in the claim 1 to 6, wherein be selected from alkali-metal hypophosphites at least a, alkali-metal phosphite, alkali-metal polyphosphate, alkali-metal phosphate, and alkali-metal sulfate, under the existence of the catalyst of the hypophosphites of preferred as alkali, described crosslinking agent and described fiber-reactive form intrafiber crosslink connection key.

8. each method in the claim 1 to 7, the water retention of wherein said cross filament is 25 to 60, preferred 30 to 45.

9. each method in the claim 1 to 8, wherein said crosslinking agent is selected from citric acid, and 1,2,3,4-butanetetra-carboxylic acid and 1,2,3-tricarballylic acid, optimization citric acid.

10. each method in the claim 1 to 8, wherein said crosslinking agent is selected from oxo two succinic acid, has the tartaric acid monobutane diacid of following structural formula:

With the two succinic acid of the tartaric acid with following structural formula:

Described crosslinking agent is preferably oxo two succinic acid.